The present invention relates generally to paper machines, and more particularly, to press sections in paper machines.
Dewatering press sections of paper machines are known having a wide pressing zone, such a press section including a press roll in conjunction with which a belt or the like is guided by guide rollers and in which press the paper or cardboard web is adapted to run in compression between the press roll and the belt. A compression fabric or fabrics act upon a respective face or faces of the web as it passes through the pressing zone. Moreover, a pressure transmitting device in the form of a unitary pressure surface or plurality of pressure shoes is provided within the loop of the belt acting in the pressing zone of the dewatering press.
In connection with the state of the art relating to the present invention, reference is made to U.S. Pat. No. 3,797,384 of Beloit Corporation of Beloit, Wis. and to U.S. Pat. No. 3,783,097, reissued as U.S. Pat. No. Re. 30,268, also of Beloit Corporation.
A press construction is disclosed in the above-identified Finnish patent application wherein water is pressed from the paper web through the use of flexible belts with a wide pressing zone being obtained by means of tensioning the belts. A drawback of this prior art "long-nip press" is that the mechanical strength of the compressing belts and their associated guide rollers imposes a limitation on the achievement of a sufficiently high pressure on the web.
A so-called long-nip press is disclosed in the above-mentioned U.S. Pat. No. 3,783,097 in which a plurality of pressure shoes are provided which press the belt against the web and press roll to achieve dewatering. However, a drawback of this structure is that the friction between the pressure shoes and the adjoining belt requires a considerable consumption of energy. Moreover, due to the friction between the belt and the pressure shoes, both the belt and shoes tend to become worn rather quickly.